Preparation method of fluoroethylene carbonate

Abstract

The invention relates to the technical field of fluoroethylene carbonate synthesis, in particular to a preparation method of fluoroethylene carbonate, which comprises the following steps: mixing hydrogen fluoride and dimethyl carbonate in proportion, and adding ethylene carbonate to prepare electrolyte; injecting the electrolyte into an electrolytic bath, and introducing direct current for electrolysis; transferring the electrolyzed mixed solution to a distillation kettle for distillation to obtain a crude product fluoroethylene carbonate; transferring the crude fluoroethylene carbonate to a crystallization kettle to obtain a crude crystal; and dissolving the coarse crystal in acetonitrile to obtain a fluoroethylene carbonate solution, and carrying out secondary crystallization through gradient cooling to obtain high-purity fluoroethylene carbonate. Through the synergistic effect of electrochemical driving and the catalyst, the high-selectivity fluorination reaction is realized, the reaction rate is increased, and the product purity is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fluoroethylene carbonate synthesis, and specifically to a preparation method of fluoroethylene carbonate. Background Art

[0002] As a new type of lithium battery electrolyte additive, fluoroethylene carbonate can form a solid electrolyte interphase membrane (SEI) with excellent performance. The SEI film directly affects the dissolution and deposition of lithium during discharge and charge, can significantly improve the cycle stability of the battery, and fluoroethylene carbonate also has the effect of reducing the flammability of lithium battery electrolytes. Therefore, it is an excellent lithium-ion battery electrolyte additive.

[0003] A common method for synthesizing fluoroethylene carbonate is to use a mixed gas of fluorine and nitrogen to react with ethylene carbonate. The raw material fluorine used in this method has the characteristics of high toxicity and high reactivity, which makes the reaction process difficult to accurately control, often accompanied by intense heat release, and the pressure in the reaction vessel increases significantly, thereby increasing the safety risk in the production process of fluoroethylene carbonate. In addition, the purity of fluoroethylene carbonate prepared by this process route is relatively low, directly affecting the final quality of the product and making it difficult to meet the strict requirements of high-quality batteries for raw materials. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a preparation method of fluoroethylene carbonate, aiming to improve the production quality of fluoroethylene carbonate. To achieve the above object, the present invention provides a preparation method of fluoroethylene carbonate, including the following steps: S1. Hydrogen fluoride and dimethyl carbonate are mixed at a volume ratio of 3:1 to 2:1 to form a homogeneous solution. Ethylene carbonate is added to the homogeneous solution, and the molar ratio of ethylene carbonate to hydrogen fluoride is controlled at 1:2 to 1:3. Based on the total mass of the system, 1 - 1.5 wt% of an additive and 0.3 - 0.5 wt% of a catalyst are added, and the mixture is stirred evenly to obtain an electrolyte solution; S2. The electrolyte solution is injected into an electrolytic cell, and a direct current is passed through for electrolysis. The current density is set at 15 mA / cm 2 , the initial cell voltage is 6.5 V, and the temperature of the electrolyte solution is maintained at 5°C; S3. The electrolyzed mixture is transferred to a distillation kettle for distillation to obtain crude fluoroethylene carbonate; S4. The crude fluoroethylene carbonate is transferred to a crystallization kettle, and fluoroethylene carbonate crystal seeds are added to induce directional crystallization. After crystallization is completed, centrifugal separation is carried out to obtain crude crystals, and the mother liquor is returned to the distillation process; S5. The crude crystals are dissolved in acetonitrile to obtain a fluoroethylene carbonate solution, and activated carbon is added for decolorization to obtain a decolorized solution; After filtering the decolorized liquid, secondary crystallization is carried out by gradient cooling to obtain high-purity fluoroethylene carbonate.

[0005] Preferably, the fluoroethylene carbonate seed crystal is 0.1-0.5% of the mass of the crude fluoroethylene carbonate.

[0006] Preferably, the mass ratio of the crude crystal to acetonitrile is 1:1-1:3.

[0007] Preferably, the dosage of the activated carbon is 2-3% of the mass of the fluoroethylene carbonate solution.

[0008] Preferably, the anode of the electrolytic cell is a nickel-based alloy electrode, and the cathode of the electrolytic cell is a nickel foam electrode.

[0009] Preferably, the electrolytic cell is connected to a circulation pump to realize dynamic circulation of the electrolyte.

[0010] Preferably, the additive is perfluoropolyether.

[0011] Preferably, the catalyst is a copper-zinc metal-organic framework catalyst.

[0012] After adopting the above technical solution, the beneficial effects of the present invention are as follows: Through the synergistic effect of electrochemical driving and the catalyst, the present invention realizes a highly selective fluorination reaction, which not only improves the reaction rate but also improves the product purity. Detailed Embodiments

[0013] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be implemented without some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by showing examples of the present invention.

[0014] Example 1 This example provides a method for preparing fluoroethylene carbonate, which includes the following steps: S1. Preparation of the electrolyte Hydrogen fluoride (HF) and dimethyl carbonate (DMC) are mixed in a volume ratio of 3:1 to form a homogeneous solution. Ethylene carbonate (EC) is added to the homogeneous solution, and the molar ratio of EC to HF is controlled at 1:2. Based on the total mass of the system, 1.5 wt% perfluoropolyether (PFPE) and 0.5 wt% copper-zinc metal-organic framework catalyst (bimetallic metal-organic framework material, CuZnMOF) are added and mixed evenly to prepare the electrolyte.

[0015] DMC can dissolve EC and promote its uniform dispersion in the electrolyte. The mixing ratio of DMC and HF can adjust the acidity of the reaction system to avoid electrode corrosion or side reactions caused by too high HF concentration. PFPE adsorbs on the electrode surface to form a protective layer, reducing the multiple attacks of fluorine radicals on EC, thereby inhibiting the formation of difluoroethylene carbonate (DFEC). DMC and PFPE work together to reduce the viscosity of the electrolyte, promote ion transport, and at the same time reduce local concentration polarization and improve the reaction uniformity.

[0016] S2. Electrolysis Prepare an electrolytic cell lined with polytetrafluoroethylene to improve the corrosion resistance of the electrolytic cell. The anode of the electrolytic cell is a nickel-based alloy electrode (such as Hastelloy C276), and the cathode of the electrolytic cell is a nickel foam electrode. The porosity of the nickel foam electrode is ≥85%, and the pore diameter is 50 - 100 μm. A 1 mm thick titanium metal backplane is attached to one side of the nickel foam electrode to enhance the mechanical strength of the electrode.

[0017] Inject the premixed electrolyte into the electrolytic cell, and control the liquid level height at 80% of the cell volume. Start the circulation pump to achieve the dynamic circulation of the electrolyte and avoid local concentration polarization. The temperature of the electrolyte in the electrolytic cell is maintained at 5 °C to inhibit side reactions through low temperature. Pass a direct current for electrolysis, and set the current density to 15 mA / cm 2 , and the initial cell voltage is 6.5 V.

[0018] In the anode region, HF dissociates to generate fluorine radicals and H + , and H + is reduced to hydrogen and escapes in the cathode region. The multi-level pore structure of the nickel foam electrode promotes the rapid escape of gas, reduces the mass transfer resistance, and avoids local concentration polarization. The Lewis acid sites of CuZnMOF adsorb and activate EC, reducing the ring tension. Fluorine radicals attack the oxygen atom of EC, and together with CuZnMOF, initiate the ring-opening reaction of cyclic carbonate to form an intermediate. The intermediate completes the ring closure in the reducing environment of the cathode region and finally forms stable fluoroethylene carbonate (FEC). Through the synergistic effect of electrochemical driving and catalyst, a highly selective fluorination reaction is achieved, which not only improves the reaction rate but also improves the product purity.

[0019] S3. Static separation After electrolysis, the mixed solution is filtered to remove the catalyst and then transferred to a temporary container. After the mixed solution stands still, due to the density and polarity differences of each component, a distinct layering phenomenon will occur. FEC has a higher density and a large polarity difference from other components of the electrolyte, so it will first settle to the bottom to form an independent liquid layer. The lower-layer liquid is extracted and transferred to a distillation kettle, and the remaining liquid is temporarily stored and reused in the electrolyte preparation process.

[0020] S4. Distillation The lower-layer liquid is transferred to a distillation kettle, and vacuum distillation is carried out at a temperature of 60 °C and a pressure of 10 kPa. The residual HF is vaporized, and the gaseous HF is recovered through a condenser. The condensed liquid HF is collected in a storage tank and used in the electrolyte preparation process. The distillation kettle is adjusted to a temperature of 60 °C and a pressure of 5 kPa for continuous distillation to distill out the residual DMC, which is collected and used in the electrolyte preparation process. Finally, the distillation kettle is adjusted to a temperature of 120 °C and a pressure of 2 kPa for distillation to distill out the residual EC, which is collected and used in the electrolyte preparation process. Through the gradient distillation kettle, crude fluorinated ethylene carbonate is obtained.

[0021] S5. Crystallization The crude fluorinated ethylene carbonate is transferred to a crystallization kettle, and fluorinated ethylene carbonate seeds accounting for 0.25% of the mass of the crude fluorinated ethylene carbonate are added to induce directional crystallization. The seeds provide nucleation sites, inhibit the formation of miscellaneous crystals, and ensure the directional growth of crystals. It is gradually cooled to 0 °C at a cooling rate of 6 °C / h to maintain a stable supersaturation degree and promote crystal growth on the surface of the seeds. After crystallization is completed, the crude crystals and the mother liquor are separated by a centrifuge, and the mother liquor is returned to the distillation process.

[0022] S6. Recrystallization The crude crystals are dissolved in acetonitrile according to a mass ratio of 1:1.5 and mixed evenly to obtain a fluorinated ethylene carbonate solution. Acetonitrile can effectively dissolve FEC in the crude crystals and has a low solubility for impurities (such as DFEC and metal ions), promoting selective precipitation. According to 2% of the mass of the fluorinated ethylene carbonate solution, activated carbon is added for decolorization to obtain a decolorized solution. After the decolorized solution is filtered to remove the activated carbon, secondary crystallization is carried out. The centrifuge separates, and the mother liquor is returned to the crystallization process to obtain fluorinated ethylene carbonate with a purity of 99.8%.

[0023] Fluorine radicals are generated by electrolyzing HF, selectively attacking the oxygen atom of EC, and activating EC by combining with the Lewis acidic sites of the CuZnMOF catalyst to achieve a directional fluorination reaction and avoid the generation of polyfluorinated by-products. EC, HF, and DMC can all be recycled, and the comprehensive cost is lower than that of traditional methods.

[0024] Example 2 This example provides a method for preparing fluorinated ethylene carbonate, including the following steps: S1. Hydrogen fluoride and dimethyl carbonate are mixed in a volume ratio of 2:1 to form a homogeneous solution. Ethylene carbonate is added to the homogeneous solution, and the molar ratio of ethylene carbonate to hydrogen fluoride is 1:2.5. Based on the total mass of the system, 1.2 wt% PFPE and 0.4 wt% CuZnMOF are added and mixed evenly to obtain an electrolyte solution. S2. The electrolyte solution is injected into an electrolytic cell and electrolyzed by passing a direct current. The current density is set to 15 mA / cm 2 , the initial cell voltage is 6.5 V, and the temperature of the electrolyte solution is maintained at 5 °C. S3. The electrolyzed mixture is transferred to a distillation still for distillation to obtain crude fluoroethylene carbonate. S4. The crude fluoroethylene carbonate is transferred to a crystallization kettle, and fluoroethylene carbonate seeds accounting for 0.1% of the mass of the crude fluoroethylene carbonate are added to induce directional crystallization. After crystallization is completed, centrifugal separation is carried out to obtain crude crystals, and the mother liquor is returned to the distillation process. S5. The crude crystals are dissolved in acetonitrile in a mass ratio of 1:1 to obtain a fluoroethylene carbonate solution. Activated carbon is added in an amount of 2.5% of the mass of the fluoroethylene carbonate solution for decolorization to obtain a decolorized solution. S6. After filtering the decolorized solution, secondary crystallization is carried out to obtain fluoroethylene carbonate with a purity of 99.3%.

[0025] Example 3 This example provides a method for preparing fluoroethylene carbonate, which includes the following steps: S1. Hydrogen fluoride and dimethyl carbonate are mixed in a volume ratio of 2.5:1 to form a homogeneous solution. Ethylene carbonate is added to the homogeneous solution, and the molar ratio of ethylene carbonate to hydrogen fluoride is 1:3. Based on the total mass of the system, 1 wt% PFPE and 0.3 wt% CuZnMOF are added and mixed evenly to obtain an electrolyte solution. S2. The electrolyte solution is injected into an electrolytic cell and electrolyzed by passing a direct current. The current density is set to 15 mA / cm 2 , the initial cell voltage is 6.5 V, and the temperature of the electrolyte solution is maintained at 5 °C. S3. The electrolyzed mixture is transferred to a distillation still for distillation to obtain crude fluoroethylene carbonate. S4. The crude fluoroethylene carbonate is transferred to a crystallization kettle, and fluoroethylene carbonate seeds accounting for 0.5% of the mass of the crude fluoroethylene carbonate are added to induce directional crystallization. After crystallization is completed, centrifugal separation is carried out to obtain crude crystals, and the mother liquor is returned to the distillation process. S5. The crude crystals are dissolved in acetonitrile in a mass ratio of 1:3 to obtain a fluoroethylene carbonate solution. Activated carbon is added in an amount of 3% of the mass of the fluoroethylene carbonate solution for decolorization to obtain a decolorized solution. After filtering the decolorized liquid, perform secondary crystallization to obtain fluorinated ethylene carbonate with a purity of 99.5%.

[0026] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to only the specific embodiments. Obviously, based on the above description, many modifications and variations can be made. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and its modified use based on the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing fluoroethylene carbonate, characterized in that: The steps include: S1, hydrogen fluoride and dimethyl carbonate are mixed in a volume ratio of 3:1 to 2:1 to form a uniform solution, ethylene carbonate is added to the uniform solution, the molar ratio of ethylene carbonate to hydrogen fluoride is controlled at 1:2 to 1:3, 1 to 1.5 wt% of additives and 0.3 to 0.5 wt% of catalyst are added based on the total mass of the system, and the mixture is mixed uniformly to prepare an electrolyte; S2, inject the electrolyte into the electrolytic cell, pass a direct current for electrolysis, and set the current density to 15mA / cm 2 , initial cell voltage 6.5V, maintain electrolyte temperature 5°C; S3, transferring the electrolyzed mixed solution to a distillation kettle for distillation to obtain crude fluoroethylene carbonate; S4, transferring the crude fluoroethylene carbonate to a crystallization kettle, adding fluoroethylene carbonate seed crystals to induce directional crystallization, centrifuging after the crystallization is completed to obtain crude crystals, and returning the mother liquor to the distillation process; S5, dissolving the crude crystals in acetonitrile to obtain a fluoroethylene carbonate solution, adding activated carbon for decolorization to obtain a decolorized solution; S6. After filtering the decolorized liquid, secondary crystallization is performed by gradient cooling to obtain high-purity fluoroethylene carbonate.

2. The method for preparing fluoroethylene carbonate according to claim 1, wherein: The fluoroethylene carbonate seed crystals account for 0.1-0.5% of the mass of the crude fluoroethylene carbonate.

3. The method for preparing fluoroethylene carbonate according to claim 1, wherein: The mass ratio of the crude crystals to acetonitrile is 1:1 to 1:

3.

4. The method for preparing fluoroethylene carbonate according to claim 1, wherein: The amount of the activated carbon used is 2-3% of the mass of the fluoroethylene carbonate solution.

5. The method for preparing fluoroethylene carbonate according to claim 1, wherein: The anode of the electrolytic cell is a nickel-based alloy electrode, and the cathode of the electrolytic cell is a nickel foam electrode.

6. The method for preparing fluoroethylene carbonate according to claim 5, wherein: The electrolytic cell is connected to a circulation pump to realize dynamic circulation of the electrolyte.

7. The method for preparing fluoroethylene carbonate according to claim 1, wherein: The additive is perfluoropolyether.

8. The method for preparing fluoroethylene carbonate according to claim 1, wherein: The catalyst is a copper-zinc metal organic framework catalyst.